Control valves are routinely used to control corresponding pneumatic or hydraulic devices in various industrial applications. Control valves can be incorporated within a complex series of valves for control of a particular manufacturing process, or control valves may be employed individually to control individual pieces of equipment. Common to all control valves is the capability of controlling the supply of a pressurized fluid to a downstream device.
Particularly in manufacturing processes, the loss of fluid system pressure can result in a catastrophic failure of the processes, and various safety devices must be incorporated within the processes to prevent failure. In many instances, the fail-safe mode for a valve dictates that the valve either remain in an open position whereby pressurized fluid may pass through the valve to the downstream device, or the fail-safe mode may dictate that the valve shut off the supply of pressurized fluid. In either case, it is desirable to use control valves which are simple, yet reliable, and can be easily returned to their normal operating modes after an alarm condition has been corrected.
One example of a prior art valve which is used within a manufacturing process for controlled delivery of fluid is U.S. Pat. No. 4,844,114. This reference discloses a pressure-drop sensor valve system for controlling the movement of a fluid operated, ram-type device, such as that used to drive a panel punch. The valve-like device includes a main passage having an inlet for pressurized fluid and an outlet connectable to the ram-type device. Disposed intermediate said inlet and outlet is a fluid chamber. A poppet valve is positioned between said fluid chamber and an accumulator chamber in the body of the device. A fluid by-pass is blocked when the poppet valve is closed and the by-pass is opened when the poppet valve is opened. A piston member is provided with its stem in the accumulator chamber opposite the poppet valve, both said member and valve being slightably movable by separate compression springs. A check valve is positioned in an axial passage of the poppet valve. The poppet valve, check valve, and piston operating in response to fluid pressure variations in the fluid passage and the accumulator chamber caused by pressure demands in the operation of the ramp so as to open the by-pass passage immediately after the punch breaks through the panel and vent pump discharge flow to the reservoir to halt further movement of the ram and punch. The poppet valve may be reset either manually or automatically.
U.S. Pat. No. 3,623,509 discloses a check valve having an internal piston member which controls the flow of pressurized fluid through the valve. The internal piston is operated by fluid flowing through a separate control loop. The piston is able to control the speed at which the check valve is opened, yet allows the check valve to close instantaneously in response to loss of fluid pressure within the fluid operating system. As disclosed in the preferred embodiment, the check valve can be moved from its seated position by contact of a push rod which is moved to disengage a main check valve part by movement of the internal piston. Fluid flowing through the control loop causes the piston to displace, and in turn, the push rod to be displaced for contacting the main check valve part.
U.S. Pat. Nos. 4,286,2 and 5,375,8, both disclose ball type check valves which are spring loaded, and can be influenced between open and closed positions by slidable pistons which contact the balls of the check valves.
Although the foregoing references may be adequate for their intended purposes, the valve of the present invention has certain advantages. Particularly in those applications in which a downstream device to be controlled only requires two positions, (such as open and closed), the valve of the current invention provides the means to effectively control such a device, and also provides a fail-safe mode in the form of an internal check element which maintains the device in its proper fail-safe position. The valve of the present invention is particularly advantageous for use with fluid cylinders. Therefore, the present invention can be also considered as a combination which includes the control valve and a cylinder in fluid communication with the valve.